Substantial quantities of olefins are produced as by-products in hydrocarbon refinery operations, particularly in cracking processes such as fluidized catalytic cracking (FCC) units and steam cracking units. The hydration of olefins to their corresponding alcohols, particularly the C4 olefins, is an industrially important reaction. Various schemes and apparatus have been proposed and adopted for optimizing the reaction conditions in order to increase the yield and/or purity of the alcohols produced.
A typical commercial processes for making 2-butanol from n-butenes operates at relatively high temperatures, i.e., in the range of 145-165° C. in order to obtain acceptable reaction rates. One problem with this type of so-called vapor phase hydration reaction is that it is equilibrium limited. That is, the olefin to alcohol reaction is reversible. This maximum rate of alcohol conversion can be as low as 5% under certain conditions as reported by Denes Kallo and R. Magdolna Mihayi in Applied Catalysis A: General 12 (1995) 45-56. In operation, however, the yields per pass are lower than the theoretical equilibrium amount, so that the yields can be even lower than the low, theoretical maximums.
In order to obtain acceptable yields for the overall process, typical commercial hydration processes recycle the stream containing the olefins. This requires an increase in the total cost of the unit and its operation, due to capital investments associated with, e.g., the compressor(s), as well as the requirement for larger reaction vessels and associated utility costs.
Other commercial processes employ mixed-phase reactions with liquid water so that the alcohol produced is continuously absorbed and the reaction is not equilibrium limited. These processes result in better yields per pass, but require high water/olefin rates and the alcohol/water solution in the reactor tend to dissolve acid catalysts employed in the reaction.
Vapor phase hydration of olefins is described in U.S. Pat. No. 2,130,669, in which olefin(s) and steam are passed through a series of liquid acidic catalyst solutions at high pressure and a temperature that results in the direct distillation of the alcohol formed. The vapors are removed from the reaction vessel and condensed. It is disclosed that a series of bubble plate reactors can be employed to sequentially treat the feed gas that will contain an ever-reduced volume of olefins. Although the examples are limited to ethylene, it is stated that the apparatus and process can be employed to convert higher olefins such as butylenes.
A proposal for improving the overall efficiency of a process for the hydration of olefins that employs a series of at least three, but possibly four or more sequential reactors in a vapor phase reaction scheme is described in U.S. Pat. No. 4,956,506. The olefin feed gas used in the process contain small amounts of ethylene and propylene olefins, i.e., between about 5% and 40% by weight based upon the total feedstream, which also includes methane, hydrogen, and/or various other gases that are inert to the hydration reaction. A suitable feed gas is said to be the tail gas from a fluid catalytic cracker. The FCC tail gas is said to typically contain from about 10 to 20 wt % of ethylene and from 4 to 10 wt % of propylene. A total of four reactors are described, each of which is packed with a perfluorinated ion-exchange polymer having pendant sulfonic and carboxylic groups. After passing through each of the reactors, the converted alcohols, i.e., ethanol and propanol, along with the unreacted feed gases are passed into a vessel containing water, which absorbs the alcohols and passes the remaining olefins and unreacted feed gases to the next reactor.
Although the examples and data reported in U.S. Pat. No. 4,956,560 are limited to the processing of ethylene and propylene, it is claimed, without examples, that butylene and pentylene can also be successfully converted and recovered using the process. However, it is well known that butanols are more soluble in organic solvents than they are in water and thus that their recovery from the process described would not be as effective as for the ethanol and propanol which are highly soluble in water. Ethanol, propanol and t-butanol are miscible with water. The solubility of 2-butanol is 35 g/100 mL at 20° C. For example, isobutanol's concentration in a mix of octyl alcohol and water is significantly different. The partition coefficient is 6.7 as reported in Collander, Acta Chemicon Scandinavica 5 (1951) 774-780.
Even though the hydration of olefins has been studied extensively, the main objective of the process of their hydration has been to produce one alcohol rather than mixed alcohols, in order to avoid complication in separation of the different alcohols produced. Prior art methods for olefin hydration are intended to produce pure alcohols. Therefore, either the olefin feed stock used in the hydration reaction must be in an essentially pure form or the hydration process has to be selective to produce only one alcohol product.
U.S. Pat. No. 4,012,456, reports that mixed butenes produce t-butanol via a selective process which hydrates iso-butene to t-butanol. The remaining isomers of butenes are not hydrated and are separated for other applications or LPG.
After removal of isobutene, other butene isomers can be further hydrated into 2-butanol, which can then be converted into methylethylketone (MEK). Mixed quantities of other products can be produced from minor constituents in the feed, such as isopropanol from propane, and side reactions with other olefins.
More recently, bio-butanol has been identified as a desirable second-generation fuel components in place of bio-ethanol. Bio-processes to produce butanols have been reported; however, the butanols are produced by bio-processes that are not particularly efficient, thereby resulting in high costs, and the amounts produced are not likely be sufficient to meet the demands of a growing butanol transportation fuel market.
Petrochemical processes for producing butanol from propylene and carbon monoxide are known, but are very costly. A need exists for an efficient and cost-effective process for producing mixed butanols by hydration.
Also needed is an efficient and cost-effective process for the production of mixed butenes from readily available butene sources in order to meet the current and foreseeable increased future demands for these products on a worldwide basis.